This invention relates to a new silage aid, process for preparation of this silage aid and use of the silage aid.
When preparing silage from for instance fish waste, the raw material is treated with acid to obtain the optimum pH (3.5-4.5) with regard to enzymatic hydrolysis, and to prevent the growth of bacteria during storage.
During the silage process hydrolysis results in the formation of emulsions made up of an acidic water phase, an oil phase and solids. The degree of phase separation in these systems depends upon the type of raw material used. Oxygen is easily transferred through water, which unfortunately gives rise to oxidative degradation of the oil phase. This lipid oxidation results, of course, in a reduced nutritional value of the oil as an ingredient both for feed and for food. Likewise, it implies a reduced quality of the oleochemicals made from fish silage oil. To overcome these problems it would be a great advantage if an antioxidant well suited for the protection of fish oil could be present during the silage process.
The most favourable way to include an antioxidant would be as a constituent of the silage aid. Generally, it would be necessary to have at least 1% antioxidant in the silage aid. Water soluble antioxidants are easily included in an acidic silage aid. Unfortunately though, these compounds will not be able to protect the oil after separation since they will not be associated with the oil phase. Furthermore, the antioxidants that are food approved in Europe and/or the US at present, are mainly fat soluble compounds. e.g. 2.6-di-tert-butyl-4-methylphenol(BHT), 3-tert-butyl-4-hydroxyanisole(BHA), tert-butylhydroquinone(TBHQ), tocopherol and the gallates. All of these food approved antioxidants are also commercially available in formulations with emulsifying agents, but unfortunately the emulsifying agents are in general hydrophobic and thus these formulations are not well suited to an acidic water medium.
The antioxidant ethoxyquin is an exception with regard to the properties described above. Ethoxyquin is a secondary cyclic amine. Hence, it is well known that ethoxyquin is soluble in acids at low pH ( less than 3), as this implies protonation of the amino croup and thereby formation of a hydrophilic salt. As pH rises to 4-5 however, ethoxyquin will be deprotonated and consequently, will again become fat soluble. Thus, by choosing the proper concentration of acid it is possible to have ethoxyquin in the form of a hydrophilic salt in the silage aid, while during the silage process the salt is deprotonated, becomes fat soluble and consequently will be able to protect the oil against lipid oxidation. Likewise, other antioxidants with an amino group may be suitable for this use. The preparation of ethoxyquin formiate salt, and this salt dissolved in formic acid is disclosed in Norwegian patent application no. 851007.
Unfortunately though, ethoxyquin or other known antioxidants with an amino group, are not food approved. Therefore, when food approval has been required, no silage aid soluble antioxidants have been available to date.
Thus it is a main object of the present invention to provide a new silage aid comprising a food approved antioxidant.
This and other objects of the invention is achieved by the attached claims.
The invention will be further explained below.
The antioxidants BHT, BHA, tocopherol, TBHQ and propyl gallate(PG) are practically insoluble in water, and experiments have shown that their solubility in mineral acids (hydrogen chloride, sulphuric acid) is also quite low (see Table 1). Unexpectedly however, we have now found that these highly hydrophobic antioxidants are soluble in the short chain caboxylic acids formic, acetic and propionic acid (see Table 1). Further experiments have shown that when using a silage aid comprising BHA, TBHQ or PG dissolved in 85% formic acid, a superior quality of the fish oil product as compared to the product of the same process using only 85% formic acid (Table 2) is obtained. When the silage aid containing antioxidant is blended with the fish waste raw material, the hydrophobic antioxidant is associated with and protects the oil phase. Thus, we have found a method which is convenient on a technical scale and which leads to superior quality of the products of the silage process.
Generally, the amount of silage aid needed will depend upon the type of fish waste used and the choice of acid. Also, the amount of antioxidant needed may depend upon the raw material used or the requirements regarding the stability of the isolated oil. This implies that the required amount of antioxidant dissolved in the acid may vary.
Furthermore, we have shown by experiments that the solubility of BHT in formic acid increases when BHA is present in the acid. This was a surprising result.
The silage aid might further comprise additives like, anti-microbiell compounds (e.g. ethyl benzoate or benzoic acid), anti-fungal compounds, anti-corrosive compounds, chelating compounds (e.g. citric acid), compounds improving the handling properties (e.g. glycerol), and oxygen scavengers.
The present invention also comprises to firstly dissolve the said antioxidants in a short chain carboxylic acid, and subsequently adding a mineral acid in the purpose of decreasing pH.
The short chain carboxylic acids according to this invention might be used either alone or in combination with their corresponding salts. Further, the aforementioned acids might be used as a mixture or as a mixture together with any of their salts.
The present invention is documented by experiments performed for a fish silage process. This invention will of course also prevail for other processes where acidic preservation is used. Fish silage shall only be considered as an example. The invention is applicable in acidic preservation of other organic by-products like slaughter waste, poultry waste and food waste, as well.